Electroless copper plating

ABSTRACT

An electroless copper plating solution comprising a source of cupric ions, hydroxyl radicals, formaldehyde or a formaldehyde precursor preferably paraformaldehyde, and a complexing agent for copper, said solution characterized by the addition of a hydrogen inclusion retarding agent and at least one member selected from the group consisting of a formaldehyde addition agent and a salt of a Group VIII metal of the Periodic Chart of the Elements. The electroless copper plating solution is capable of providing a rapid rate of copper deposition dependent upon the selection of the complexing agent without sacrifice in tensile properties of the copper deposit. The copper plate deposited from the electroless solution of this invention is distinguishable from prior art electroless copper deposits by substantially improved bending or ductility properties.

United States Patent 16 Claims, No Drawings U.S. Cl 106/1, 117/47,117/130, 117/160 Int. Cl C23c 3/02 Field of Search 106/ 1; 117/130 E,130,47 R, 35 S, 213, 227

References Cited UNITED STATES PATENTS 3,093,509 6/1963 Wein 117/35 X5/1964 Eriksson 1 17/47 X Inventors Appl. No.

Filed Patented Assignee Charles R. Shipley, Jr.

Newton;

Lucia l-l. Shipley, Newton; Michael Gulla, Newton; Oleh B. Dutkewych,Medfield, all of Mass.

Aug. 13, 1968 Oct. 26, 197 1 Shipley Company, Inc.

Newton, Mass.

ELECTROLESS COPPER PLATING 3,310,430 3/1967 Schneble et al 106/1 X3,329,512 7/1967 Shipley et a]. 106/1 FOREIGN PATENTS 401,083 1/1965Japan 106/1 Primary Examiner-Lorenzo B. Hayes Attorney-Roberts, Cushmanand Grover ABSTRACT: An electroless copper plating solution comprising asource of cupric ions, hydroxyl radicals, formaldehyde or a formaldehydeprecursor preferably paraformaldehyde, and a complexing agent forcopper, said solution characterized by the addition of a hydrogeninclusion retarding agent and at least one member selected from thegroup consisting of a formaldehyde addition agent and a salt of a GroupVlll metal of the Periodic Chart of the Elements. The electroless copperplating solution is capable of providing a rapid rate of copperdeposition dependent upon the selection of the complexing agent withoutsacrifice in tensile properties of the copper deposit. The copper platedeposited from the electroless solution of this invention isdistinguishable from prior art electroless copper deposits bysubstantially improved bending or duetility properties.

ELECTROLESS COPPER PLATING BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a metal depositing composition andmore particularly to an electroless copper plating solution capable ofproviding electroless copper deposit of improved bending or ductilityproperties.

2. Description of the Prior Art Electroless copper deposition refers tothe chemical plating of copper over clean catalytically active surfacesby chemical reduction in the absence of an external electric current.Such processes and compositions useful therefor are known and are insubstantial commercial use. They are disclosed in a number of prior artpatents, for example, U.S. Pat. Nos. 2,938,805; 3,01 1,920; 3,310,430and 3,383,224.

Known electroless copper deposition solutions generally comprise fouringredients dissolved in water. They are (l) a source of cupric ions,usually a copper salt, such as copper sulfate, (2) a reducing agent suchas formaldehyde, or preferably a formaldehyde precursor such asparaformaldehyde, (3) free hydroxide, generally an alkali metalhydroxide and usually sodium hydroxide, sufficient to provide therequired alkaline solution in which said compositions are effective, and(4) a complexing agent for copper sufficient to prevent itsprecipitation on alkaline solution. A large number of suitablecomplexing agents are known and described in the above-cited patents,and also in U.S. Pat. Nos. 2,874,072; 3,075,856; 3,119,709; 3,075,855,and 3,329,512 all incorporated herein by reference. Known electrolessplating solutions of the above type usually provide a plate which, ifmechanically dense and strong, is somewhat brittle such that it canwithstand only limited bending or thermal stress without fracture. Thisis not a substantial disadvantage where the electroless plate is of theorder of millionths of an inch in thickness and is overplated withductile electrolytic copper. However, where the entire desiredthickness, typically 1 to 3 mils in an electrical application, isprovided by electroless plating, limited ductility is a seriouslimitation.

One means for improving the tensile properties of an electroless copperdeposit while simultaneously improving brightness and other appearanceproperties is described in U.S. Pat. 3,475,186 filed Jan. 5, 1968, andincorporated herein by reference. lmproved properties are obtained bythe addition of an organic silicon compound to be electroless coppersolution where silicon is believed to be the active agent. A majoradvantage of this system is that the rate of copper deposition does notsubstantially affect tensile properties. The manner in which the siliconcompound improves tensile properties is not fully understood but it isbelieved to be due, at least in part, to a surface effect resulting indeposition of a smoother deposit having fewer structural defects.

An improved method for improving tensile properties is set forth incopending U.S. Pat. application Ser. No. 752,250 filed concurrentlyherewith. In a preferred embodiment, a combination of additivescomprising a silicon compound, a formaldehyde addition agent, and a saltof a Group Vlll metal of the Periodic Chart of the Elements is added tothe electroless copper bath. Electroless copper deposited from said bathis characterized by substantially improved tensile properties resultingfrom a synergistic reaction between the additives and possessesincreased tensile properties, improved brightness and substantiallyimproved solderability.

An additional method for improving the bending or tensile properties ofan electroless copper plate using a difi'erent mechanism is described inU.S. Pat. No. 3,310,430, which discloses the addition to a copperplating solution of a water soluble compound of cyanide, vanadium,molybdenum, niobium, tungsten, arsenic, antimony, bismuth, rare earthsof the actinium series and rare earths of the lanthanum series. Certainmembers of the group, especially the vanadium compounds, providesignificantly improved bending characteristics. The reason for this isnot fully understood but it is stated in the patent that the agentspoison the catalytic surface so as to promote formation and release ofhydrogen at the catalytic surface, thereby inhibiting the inclusion inthe deposit as it forms. It has been found that where a complexing agentor a bath formulation is used permitting rapid deposition of copper withrapid evolution of hydrogen gas at the surface, the im-' provedductility or bending characteristics are frequently sacrificed or lost.

STATEMENT OF THE INVENTION The subject invention is an improvement overthat described in the above-noted U.S. Pat. No. 3,310,430 in that itavoids the disadvantages noted above and provides an electroless coppersolution capable of depositing an electroless copper plate havingsubstantially improved bending or tensile properties regardless of therate of copper deposition and the complexing agent used. The coppersolution is characterized by the addition of a hydrogen inclusionretarding agent and at least one member selected from the groupconsisting of a formaldehyde addition agent, and a salt of a Group Vlllmetal of the Periodic Chart of the Elements. In addition to animprovement in bending or tensile; properties, electroless copperdeposits from the solutions of this invention provide the furtheradvantages of excellent laydown properties, and excellent solderabilityalong with improvement in smoothness, brightness and overall appearance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical electroless coppersolution in accordance with the invention will have additivesiin thefollowing concentration ranges:

Water to 1 liter of solution It should be understood that the aboveconcentration ranges are preferred but not critical. Variations in theranges are possible without varying from the scope of the invention. Inmost cases, additives may be added in any amount up to that amount thatpoisons the solution and prevents deposition.

In the above formulations, any water soluble copper salt heretofore usedfor preparing electroless copper deposition solutions may be used. Forexample, certain of the halides, nitrate, acetate, sulfate, and otherorganic and inorganic acid salts of copper are generally suitable as isknown in the art. Copper sulfate is preferred.

Suitable complexing agents for the copper ions are well known in the artand include Rochelle salts, the sodium salts (mono-, di tri-, andtetrasodium salts) of ethylenediaminetetraacetic acid, nitrilotriaceticacid and its alkali metal salts, triethanolamine, modifiedethylenediaminetetraacetic acids such asN-hydroxyethylenediaminetriacetate, hydroxyalkyl substituted dialkylenetriamines such as pentahydroxypropyldiethylenetriamine, sodiumsalicylate, and sodium tartrate.

Othes complexing agents for copper ions are disclosed in U.S. Pat. Nos.2,996,408; 3,075,855; 3,075,856 and 2,938,805.

The preferred class of complexing agents are those described in US. Pat.No. 3,329,512 noted above. They include hydroxyalkyl substitutedtertiary amines corresponding to one of the following structures:

R011 and ROE where R is an alkyl group having from two to four carbonatoms, R is a lower alkylene radical and n is a positive integer.Examples of these complexing agents include tetrahydroxypropyl ethylenediamine, pentahydroxypropyl diethylene triamine, trihydroxypropylamine(tripropanolamine),

0 ing Company, Third Edition 1964, pages 219 to 22 I, includedtrihydroxypropyl hydroxyethyl ethylene diamine, etc. As disclosed insaid patent, the aforesaid amines are preferably used in small amountsin combination with other complexing agents and with certain polymersdispersed in solution such as cellulose ethers, hydroxyethyl starch,polyvinyl alcohol, polyvinylpyrrolidone, peptones, gelatin, polyamidesand polyacrylamides.

The rate of copper deposition is, to some extent, dependent upon theselection of the complexing agent. Complexing agents such aspentahydroxypropyldiethylenetriamine provide a rapid rate of copperdeposition, usually in excess of 1.0 mils per hour. Though the coppersolutions of this invention provide copper deposits from solutionscontaining any of the known complexing agents for copper ions, they areparticularly well adapted for copper solution having complexing agentsthat provide a rapid rate of copper deposition.

The hydrogen inclusion retarding agent is of the same class disclosed inthe above-noted US. Pat. No. 3,310,430 and includes simple and complexcompounds which comprise one or more of cyanide, vanadium, molybdenum,niobium, tungsten, rhenium, arsenic, antimony, bismuth, actinium,lanthanum, rare earths of both the lanthanum and actinium series andmixtures of the foregoing.

Preferred are those compounds which consist of or comprise elements ofthe type described which have at least two oxidation states. In thispreferred group are compounds comprising vanadium, niobium, molybdenum,tungsten, rhenium, arsenic, antimony, bismuth, cerium, praseodymium,neodymium, Samarium, europium, terbium, uranium, and mixtures of theforegoing. These elements are preferably added to the electroless copperplating baths in a form such that the element is at its most stablevalence state. Vanadium and cyanide are the most preferred hydrogeninclusion retarding agents. Where cyanide is selected as the hydrogeninclusion retarding agent, it may appear twice in the formulationdependent upon the selection of the remaining additives.

The hydrogen inclusion retarding agent is added to the bath, preferablyas a soluble salt. For example, molybdenum may be supplied as molybdictrioxide as well as water soluble organic and inorganic acid salts ofmolybdenum, as for example alkali and alkaline earth metal, or ammoniummolybdates. Suitable sources of tungsten, molybdenum, rhenium, andarsenic are the oxides of such elements, as well as organic andinorganic acid water soluble salts of such elements, e.g., thetungstates, vanadates, arsenates, and rhenates of the metals of GroupsLA and lI-A of the Periodic Chart of the Elements, and ammonium.Preferred for use are the sodium, potassium, and ammonium salts. Sourcesof antimony, bismuth, lanthanum, actinium, and rare earths are theoxides of such elements and water soluble organic and inorganic acidsalts of such elements, including the sulfates, nitrates, halides,acetates, and the like. The function of the hydrogen inclusion retardingagent is not fully understood, but it is reported that it tends topoison the catalytic surface so as to promote the formation and releaseof hydrogen gas at the catalytic surface on which copper is herein byreference. Preferred formaldehyde addition agents include alkali andalkaline earth metal sulfites, bisulfites, and phosphites of a metalcation that does not codeposit with copper and preferably, an alkalimetal cation. Preferred formaldehyde addition agents are sodium sulfite,sodium bisulfite, potassium sulfite and sodium phosphite.

The formaldehyde addition agent and formaldehyde or preferably,paraformaldehyde are reacted with each other to form the adduct prior toaddition to the remaining components of the copper solution.

The Group VIII metal salts are preferably water soluble inorganic saltsof iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium,and platinum; salts of nickel, iron and platinum being most preferredand salts of palladium being least preferred clue to solution stabilityproblems caused by palladium. Suitable salts include phosphates,nitrates, halides, and acetates, of the above metals.

The cyanide compound is a water soluble compound such as an alkali metalcyanide, such as sodium cyanide, potassium cyanide, sodium nitrile,potassium nitrile, organic nitriles such as alphahydroxynitrile, e.g.,glycolnitrile and lactonitrile, and dinitriles, such asiminodiacetonitrile and 3,3 iminodipropionitrile.

A wetting agent may be added to solution in accordance with artrecognized procedure.

The bath may be used at widely varying temperatures, e.g., at least roomtemperature and preferably up to F. As temperature is increased, it iscustomary to find an increase in the rate of plating. Temperature is nothighly critical and within the usual operating ranges, excellent, brightdeposits of electroless copper having excellent ductility properties areobtained. Preferably, the bath is used without agitation.

in using the electroless copper solution to plate metal, the surface tobe plated should be catalytically active and free of grease andcontaminating material. Where a nonmetallic surface is to be plated, thesurface area to receive the deposit must first be sensitized to renderit catalytically active as by the well-known treatment with an acidicaqueous solution of stannous chloride followed by treatment with adilute aqueous acidic solution of palladium chloride. Alternatively,extremely good sensitization of nonmetallic surfaces is achieved bycontact with an acidic colloidal formulation formed by the admixture ofstannous chloride and a precious metal chloride, preferably palladiumchloride, the stannous chloride being present in stoichiometric excessbased upon the amount of precious metal chloride.

The invention will be better understood by reference to the followingexamples where all parts were plated using the following procedure:

a. Cut a phenolic substrate to a size of 2" X2.

b. Scrub part clean using an abrasive cleaner.

c. Rinse in cold water.

d. Immerse in a solution of a wetting agent identified as ShipleyConditioner 1159 at room temperature for l to 3 minutes.

e. Rinse in cold water.

f. Immerse in a colloidal stannic acid-palladium catalyst (identified asCuposit Catalyst 6F) maintained at room temperature for l to 5 minutes.

g. Rinse in cold water.

h. Immerse in a Cuposit Accelerator 19 or a mild perchloric acidsolution maintained at room temperature for 3 to 10 minutes.

i. Rinse in cold water.

j. linmerse in electroless copper solution maintained at between 110 and130 F. for a period sufficient to provide a deposit of desired thicknessnot to exceed 3 hours.

k. Dry parts and analyze the deposit for appearance and ductility.Ductility is determined by peeling a copper deposit from the substrateand bending it through 180 F. in one direction, creasing at the fold,then returning it to its original position with pressing along thecrease to flatten it. This cycle constitutes one bend. The procedure isrepeated until the sample breaks at the crease. A sample unable towithstand at least one-half bend is considered brittle.

EXAMPLES l-20 CuSOflLO 8.0 g. Paraforrnaldehyde 7.5 g.

NaDH (25% solution by wt.) 50.0 ml. Tetrahydroxypropylethylene amine12.0 g. Triisopropanoldiamine 2.0 g.

Water to l l. of solution The above formulation, with various additives,is used to deposit electroless copper. Additive compositions and depositproperties are set forth in the following table:

EXAMPLES 21-25 CuS -5H 0 8.0 gm. Paraiormaidehyde. 7.5 gm.

NaOH (25% solution) 50.0 ml. Ethylenediaminetetraacetic acid.. 30.0 gm.

Water To 1 liter oi solution.

The above formulation, with various additives, is used to depositelectroless copper. Additive composition and deposit properties are setforth in the following table:

Deposit Ex. Additive Deposit thickness Ductility No. Additiveconcentration appearance in.X-' (bends) 0.19 Brittle. 0.29 Do.

7 555,516 of the above represents a substantial improvement in tensileproperties.

Deposit Deposit appearance Additive Example concentration numberAdditive thickness, in. 10"

Ductility (bends) Deposit Deposit appearauce Additive concentrationExample number Additive thickness, ln.)(10' Ductility (bends) Nazsoa 8Brittle.

in the above examples, a deposit was considered poor if it was dark incolor and powdery. A fair deposit was one lighter in color thoughpowdery in appearance. A good deposit was one having a fine grainedmetallic copper appearance.

The improvements in tensile properties using the electroless coppersolutions of the present invention are readily apparent by reference bythe above examples. Examples 2 to 4 illustrate copper solutionscontaining only a hydrogen inclusion retarding agent. Examples 5 toillustrate copper solutions containing only a Group VIII metal salt.Examples 10 to 12 illustrate copper solutions containing only aformaldehyde addition agent. Using any of these single additives alone,little or no improvement in tensile properties is obtained. In examples13 to 17, there is represented combinations of two additives resultingin minor improvements in tensile properties. Examples 18 to 20 representdeposits formed from solutions of the subject invention and illustrate aminimum of a 300 percent increase EXAMPLES 26-29 CuSO4-5H10 8.0 gm.Formaldehyde 7.5 gm. NaOH (25% solution). Sodium/potassium tartrate.

03 l0 .p.m.

............................ To 1 liter of solution.

m ThESEdv formulation, with various additives, is used to depositelectroless copper. Additive compositions and deposit properties are setforth in the following table:

In the above, example 26 represents a poor control sample because of thethinness of the deposit. A thicker deposit would probably be brittle.However, the combination of the hydrogen inclusion retarding agent,Group VIII metal salt and formaldehyde addition agent provides depositssubstantially improved over that of the control capable of withstandingin excess of five bends without fracturing.

Copper solutions of this invention find utility for all purposes forwhich electroless copper solutions have heretofore been used includingboth decorative and industrial applications. They are especially usefulfor the formation of printed circuit boards where the deposit acts as aductile conductor both in a circuit pattern and on the walls ofthrough-holes. The formation of a printed circuit board havingconductive through-holes is illustrated in the following example:

V EXQMPLE 30 I a. Sandblast one side of a phenolic substrate leaving thesecond surface smooth.

b. Drill through-holes at desired locations.

c. Silk screen a reverse image of a printed circuit pattern onto theroughened surface of the phenolic substrate using an epoxy resin resist.

d. Immerse in a colloidal palladium sensitizing solution maintained atroom temperature for a period of minutes.

e. Immerse in a stripping solution comprising 10 grams of copperchloride, 100 grams of 37 percent hydrochloric acid, and water to 1liter. Maintain stripping solution at room temperature and immerse partin solution for 6 minutes.

f. Deposit electroless copper of example 25 with copper depositiontaking place on the walls of the through-holes and on the roughenedsurfaces in an image pattern. No copper deposition takes place on theepoxy resist or on the smooth side of the plastic laminate.

The mechanism by which copper deposits from the solution of thisinvention differs from that of the above referenced U.S. Pat. No.3,310,430 where hydrogen inclusion retarding agents alone are used toimprove ductility. Though neither mechanism is fully understood, adifferent mechanism is sug gested by the observation that the Group VIIImetal cation codeposits with copper, to some extent, in the absence of ahydrogen inclusion retarding agent but codeposition is lessened when ahydrogen inclusion retarding agent is in solution. This is shown by thefollowing examples:

EXAMPLES 31-32 The copper deposits of the above examples were analyzed.

In example 31 containing both vanadium and nickel compounds in solution,only 0.00088 percent nickel was found in the deposit. Omission of thevanadium compound in example 32 results in a copper deposit containing0.100 percent nickel. This indicates that the vanadium somehow retardedthe codeposition of nickel.

It should be understood that various changes may be made in theembodiments described above without departing from the spirit and scopeof the invention as defined by the following claims:

We claim:

1. In an electroless copper plating solution comprising a source ofcupric ions, hydroxyl radicals, formaldehyde and sufficient complexingagent to render said cupric ions soluble in alkaline solution, theimprovement comprising an additive in solution of at least one hydrogeninclusion retarding agent in an amount of from 1 to 1,000 parts permillion parts of solution, said hydrogen inclusion retarding agent beingselected from the group consisting of solution soluble compounds ofalkali and alkaline earth metal cyanides and nitriles, vanadium,molybdenum, niobium, tungsten, rhodium, arsenic, antimony, bismuth, rareearths of the actinium series, rare earths of the lanthanum series andmixtures thereof; and at least one solution soluble member selected fromthe group consisting of a formaldehyde addition agent in an amount offrom 0.1 moles times the moles of formaldehyde to 1 times the moles offormaldehyde, said agent being selected from the group consisting ofalkali metal sulfites, bisulfites, and phosphites; and a salt of amember selected from the group of iron, nickel, and platinum in anamount of from 5 to 2500 parts per million parts of solution, said salthaving an anion noninterfering with 0.02 to 0.l2 moles 0.l to l moles lto 3 times the moles of cupric ion 0.l to 0.8 moles copper saltformaldehyde complexing agent free hydroxide hydrogen inclusionretarding agent 5 to 250 p.p.l'n. formaldehyde addition 0.I to I timesthe moles agent of formaldehyde Group VIII metal salt 30 to I000 p.p.m.Water to l liter of solution 6. The copper plating solution of claim Iwhere the cyanide compound is sodium cyanide.

7. The copper plating solution of claim 1 where the hydrogen inclusionretarding agent is As,0,.

8. The copper plating solution of claim I where the hydrogen inclusionretarding agent is V 0 9. In an electroless copper solution comprising asource of cupric ions, hydroxyl radicals, formaldehyde and sufficientcomplexing agent to render said cupric ions soluble in alkalinesolution, the improvement comprising an additive in the solutioncomprising at least one hydrogen inclusion retarding agent and at leastone solution soluble member selected from the group consisting of aformaldehyde addition agent and a salt of a Group VIII metal of thePeriodic Chart of the Elements; said hydrogen inclusion retarding agent,and Group VIII metal salt being present in solution in minor amountssufficient to improve ductility of a copper deposit and said formaldehyde addition agent being present in an amount of from 0.1 molesper mole of formaldehyde to that amount that restricts copperdeposition.

10. The copper plating solution of claim 9 having as additive at leastone hydrogen inclusion retarding agent, and the Group VIII metal salt.

11. The copper plating solution of claim 9 having as additive at leastone hydrogen inclusion retarding agent and the formaldeh de additionagent.

12. e copper plating solution of claim 9 having as additive the hydrogeninclusion retarding agent, the formaldehyde addition agent and the saltof the Group VIII metal.

13. The copper plating solution of claim 9 where the salt of the GroupVIII metal is selected from the group consisting of NiSO Fe (SO and HPtCI 14. The copper solution of claim 9 where the formaldehyde additionagent is selected from the group consisting of Na SO NaI-ISO and NaI-IPO 5H O.

15. The copper plating solution of claim 9 where the hydrogen inclusionretarding agent is NaCN.

16. The copper plating solution of claim 9 where the hydrogen inclusionretarding agent is selected from the group consisting of V 0 and AsO,-,.

2. The copper plating solution of claim 1 having as additive at leastone hydrogen inclusion retarding agent and a salt of a Group VIII metal.3. The copper plating solution of claim 1 having as additive at leastone hydrogen inclusion retarding agent and a formaldehyde additionagent.
 4. The copper plating solution of claim 1 having as additive atleast one hydrogen inclusion retarding agent, a salt of a Group VIIImetal and a formaldehyde addition agent.
 5. The copper plating solutionof claim 1 having the following formulation: copper salt 0.02 to 0.12moles formaldehyde 0.1 to 1 moles complexing agent 1 to 3 times themoles of cupric ion free hydroxide 0.1 to 0.8 moles hydrogen inclusionretarding agent 5 to 250 p.p.m. formaldehyde addition 0.1 to 1 times themoles agent of formaldehyde Group VIII metal salt 30 to 1000 p.p.m.Water to 1 liter of solution
 6. The copper plating solution of claim 1where the cyanide compound is sodium cyanide.
 7. The copper platingsolution of claim 1 where the hydrogen inclusion retarding agent isAs2O3.
 8. The copper plating solution of claim 1 where the hydrogeninclusion retarding agent is V2O5.
 9. In an electroless copper solutioncomprising a source of cupric ions, hydroxyl radicals, formaldehyde Andsufficient complexing agent to render said cupric ions soluble inalkaline solution, the improvement comprising an additive in thesolution comprising at least one hydrogen inclusion retarding agent andat least one solution soluble member selected from the group consistingof a formaldehyde addition agent and a salt of a Group VIII metal of thePeriodic Chart of the Elements; said hydrogen inclusion retarding agent,and Group VIII metal salt being present in solution in minor amountssufficient to improve ductility of a copper deposit and saidformaldehyde addition agent being present in an amount of from 0.1 molesper mole of formaldehyde to that amount that restricts copperdeposition.
 10. The copper plating solution of claim 9 having asadditive at least one hydrogen inclusion retarding agent, and the GroupVIII metal salt.
 11. The copper plating solution of claim 9 having asadditive at least one hydrogen inclusion retarding agent and theformaldehyde addition agent.
 12. The copper plating solution of claim 9having as additive the hydrogen inclusion retarding agent, theformaldehyde addition agent and the salt of the Group VIII metal. 13.The copper plating solution of claim 9 where the salt of the Group VIIImetal is selected from the group consisting of NiSO4, Fe2(SO4)3 andH2PtCl6.
 14. The copper solution of claim 9 where the formaldehydeaddition agent is selected from the group consisting of Na2SO3, NaHSO3,and Na2HPO3.5H2O.
 15. The copper plating solution of claim 9 where thehydrogen inclusion retarding agent is NaCN.
 16. The copper platingsolution of claim 9 where the hydrogen inclusion retarding agent isselected from the group consisting of V2O5 and As2O3.